The present invention relates to a source of electrical pulses; and more particularly, the invention relates to the production of electrical pulses pursuant to measuring position and/or speed and/or direction of moving machine parts.
Transducers of the type which produce measuring pulses are, for example, constructed to include a source of radiation (e.g., light), an optical-electronic pickup and scanner, and a diaphragm such as a slotted disk, i.e., an optical grating. The rotation of the disk presents the motion to be analyzed and divides that motion into a plurality of well-defined individual steps. The motion to be analyzed may be directly rotational in character or a translatory motion converted into rotation for purposes of transduction and measurement. Alternatively, linear gratings have been used for that purpose. Of particular interest is the field of matrix printer, and, here particularly, the motion of the print head on a carriage across the sheet to be printed on; paper-feeding devices; etc.
The individual steps referred to above are represented as pulses, whereby particularly the speed of the machine part is represented by the pulse rate frequency, and each pulse represents a particular position of that part. Refinement of the transduction permits also the production of two pulse trains whose relative phase may represent the direction of movement. Equipment of this kind includes usually a counter for purposes of acquiring exact data on position, speed and/or the direction of motion.
The double-pulse train method for purposes of direction-finding usually involves a phase shift of 90.degree. between the pulses of the two trains, and the distinction between lagging and leading establishes the requisite directional information. Usually, one uses here two light sources and two detectors. The resulting two detection channels and light barriers are sufficiently offset to avoid interference. In view of the similarity and strict periodicity of the slots, it is not necessary that these channels be offset by 90.degree. in relation to the same slot; but the offset may additionally involve an integral multiple of the slotspacing. It was found that the structure, realizing such a concept, is, in fact, very complicated and expensive particularly in regard to adjustment but also in regard to manufacture and installation because one needs to adjust the phase shift quite exactly to 90.degree..
German printed patent application 23 93 874 (see also U.S. Pat. No. 3,902,063) describes a photoelectric scanner, in which two detector-scanners are mounted on a carrier which is rotatable about an axis extending between the two scanners. These two scanners are associated with a common detection field. The carrier is provided with adjustment slots being concentric to that axis, and screws traversing these slots fasten the carrier in an adjusted position. This device is very expensive, in particular regarding the angular adjustment feature. Furthermore, manufacture and installation require extremely low tolerances. Moreover, the adjustment requires three screws just for arresting the carrier in the adjusted position, and again they must meet very close tolerances. This approach is not deemed desirable; particularly, the expense is not justified in relation to actually attainable accuracy.